This invention relates to compositions which are useful for enhancing adhesion of adhesives, sealants, and coatings to various substrates including metals such as aluminum and steel, rubber, glass, plastics, and wood or combinations thereof. The adhesive bond formed to the substrate must be able to maintain its integrity upon exposure to aggressive environments such as exposure to heat, moisture, salt spray, solvents, and acids. In the specific instance of adhesives, stresses which are placed upon the bonded assembly must not be allowed to cause adhesive failure.
Adhesives, sealants, and coatings are closely related products all requiring excellent adhesion. Most fundamentally, an adhesive is used to bond two surfaces together so that the assembly may withstand stress, a sealant is used to cover a boundary where two or more materials meet, and a coating is used to both protect a single type of material from the deleterious effects of the environment and also to enhance surface aesthetics.
It is recognized by those skilled in the art that such adhesives may include epoxys, phenolics, and various elastomeric resins such as nitrile, neoprene, vinyl butyural, SBR, EPDM, polyurethane, silicone, and styrene butadiene block copolymers.
Sealants are compositionally related to adhesives and may include polyurethanes, polyvinyl chloride plastisols, vinyl, nitrile, EPDM, silicone, neoprene, SBR, styrene/butadiene block copolymers, and water based systems such as SBR, acrylic or polyvinyl acetate. The sealant is actually a thick coating which must additionally be able to respond to stresses placed upon the joined components without rupture; hence, unlike coatings they are generally elastomeric.
High performance coatings are formulated primarily to protect surfaces against aggressive environmental agents. Of the three classes of materials, coatings is unique in having little concern regarding withstanding stresses. Hence, coating resins encompass a different set of resins including alkyds, acrylic, epoxy, epoxyester, saturated polyester/melamine, unsaturated polyester, polyurethane, silicones, vinyl, and vinyl toluene.
Sealant and adhesive manufacturers have historically used silanes to enhance adhesion. The usefulness of silanes is in part mitigated by their high cost, difficulty in handling owing to water sensitivity, and the limiting specificity of silane containing adhesives and sealants for certain substrate types, i.e., glass rubber, and only marginally metals.
The compositions described herein are related to aluminum zirconium metallo organic complexes described in U.S. Pat. Nos. 4,539,048 and 4,539,049. Unlike the predecessor complexes, the subject compositions have multiple organofunctional groups in each molecule which contains a minimum of one amine group. Such compositions may not be synthesized in accordance with the teachings of the prior art due to the high reactivity of the organofunctional groups which induce inorganic polymerization; hence, the multifunctional amino zirconium aluminum complexes of the present invention may only be synthesized utilizing the process technology described herein, i.e., in a solvent which is capable of chelating with the metals and thus prevents the polymerization of the Al and Zr species.